1. Field of the Invention
The subject invention relates to a device and method for filling a conventional disposable plastic syringe with a mixture of insulins.
2. Description of Related Art
Hypodermic syringes are used to deliver selected doses of medication to patients. The prior art hypodermic syringe includes a syringe barrel having opposed proximal and distal ends. A cylindrical chamber wall extends between the ends and defines a fluid receiving chamber. The proximal end of the prior art syringe barrel is substantially open and receives a plunger in sliding fluid fight engagement. The distal end of the prior art syringe barrel includes a passage communicating with the chamber. A needle cannula may be mounted to the distal end of the prior art syringe barrel, such that the lumen of the needle cannula communicates with the passage and the chamber of the syringe barrel. Movement of the plunger in a proximal direction draws fluid through the lumen of the needle cannula and into the chamber. Movement of the plunger in a proximal-to-distal direction urges fluid from the chamber and through the lumen of the needle cannula.
Medication to be injected with the prior art hypodermic syringe is commonly stored in a vial having a pierceable elastomeric seal and accessed by piercing the elastomeric seal with the needle cannula of the syringe. A selected dose of the medication is drawn into the chamber of the syringe barrel by moving the plunger of the syringe a selected distance in a proximal direction. The needle cannula is then withdrawn from the vial and the medication is injected into a patient by moving the plunger in a distal direction.
Some medication, such as insulin, is self-administered and a typical diabetes patient will require injections of insulin several times during the course of the day. The required dose of insulin will vary from patient to patient, and for each patient may vary during the course of the day and from day to day. Each diabetes patient will establish a regimen that is appropriate for his or her own medical condition and for his or her lifestyle. Sometimes the regimen will include some combination of a slow acting (Regular) insulin and an intermediate acting (NPH) insulin which may require the diabetes patient to periodically mix and/or self-administer insulin in public locations, such as places of employment or restaurants. The manipulation required to do this using the standard prior art hypodermic syringe and vial can be inconvenient and embarrassing in these public environments.
Normally, insulin "free-mixing" is performed with two 10 ml vials (not cartridges) of insulin sealed with a rubber septum. The first step involves adding a volume of air to each vial that is equal to the insulin volume to be removed. This is important to prevent an ever-increasing vacuum in the vial as insulin is removed. Next, a conventional disposable syringe is inserted in a NPH vial and the desired volume (units) is drawn up. If too much is drawn into the syringe, the excess can be returned to the NPH vial. The syringe is then inserted into a Regular vial and a mental calculation is made to determine the amount of draw since the target syringe scale is not reading the Regular insulin dose alone, but the sum of NPH and Regular. If too much Regular insulin is drawn into the syringe, the syringe contents must be totally discarded and the entire process restarted. The contents needs to be discarded since the syringe contains some NPH insulin which can not be returned to the Regular vial. Therefore, the above process is by no means easy to do and is also complicated by the fact that people with diabetes frequently have vision problems, manual dexterity problems or both.
Because of the difficulty in "free-mixing" with vials, physicians often prescribe a pre-mixture of the two types of insulin, which are combined by drug companies into one vial. However, pre-mixtures are infrequently made at the desired ratio for all patients and are not compatible with the frequent adjustments necessary for "tight" glycemic control. It is not possible to change the dose on one type of insulin without simultaneously changing the other insulin component in such a pre-mixture.
Medication delivery pens offer certain conveniences over syringes to the patient who is required to self-administer medication, i.e., less embarrassment. However, the insulin containing cartridges used in such pens are also not readily available in all the pre-mix ratios that are required by diabetic patients that must mix their insulin. Therefore, there is the need to provide a device and/or method that makes it easier for a diabetic patient to carry, mix and load a syringe with the mixed insulin when performing such injections.